This invention relates to optical digital circuits and, more particularly, to an optical linear feedback shift register.
All-optical information processing holds promise for processing throughput rates which are much faster than electronics. Despite its relatively weak nonlinear index, silica optical fiber remains the most promising medium for realizing all-optical processing systems. The loss is low enough that extremely long lengths can be used to compensate for the weak nonlinearity, and there is vast amount of existing technology that can be exploited in building a system. All-optical fiber Sagnac interferometer switches have been demonstrated in a number of different formats, and at extremely high speeds. Such Sagnac switches are extremely simple structures which are also immune to fluctuations in ambient conditions, and much experience has been accumulated in the development of Sagnac-based fiber optic gyroscopes.
To build an optical three-terminal Sagnac switch, a control beam must be used which is isolated from a separate signal beam. Two distinct optical wavelengths can be used, in which case lossless combination and separation of the control and signal can be effected using wavelength dependent couplers or filters. While the use of different wavelengths is an elegant scheme for a simple system, the complexity grows as the system grows in complexity, because identical devices of this type cannot be cascaded. Recently, a polarization-based Sagnac switch was demonstrated, in which polarization rather than wavelength was used to distinguish the control beam from the signal beam. Stable polarization-based interferometry is achieved in a Sagnac switch by using polarizing couplers.
Notwithstanding the progress made in implementing optical switches, before an all-optical information processing apparatus becomes a reality, a number of other electronic circuit functions need to be implemented in an optical environment.